Storage stability problems are well known with liquids containing enzyme(s). Especially in enzyme-containing liquid detergents a major problem, in particular if the detergent contains protease, is that of ensuring enzyme activity over time.
The prior art has dealt extensively with improving the storage stability, for example by adding a protease inhibitor.
Boric acid and boronic acids are known to reversibly inhibit proteolytic enzymes. A discussion of the inhibition of one serine protease, subtilisin, by boronic acid is provided in Molecular & Cellular Biochemistry 51, 1983, pp. 5-32.
Boronic acids have very different capacities as subtilisin inhibitors. Boronic acids containing only alkyl groups such as methyl, butyl or 2-cyclohexylethyl are poor inhibitors with methylboronic acid as the poorest inhibitor, whereas boronic acids bearing aromatic groups such as phenyl, 4-methoxyphenyl or 3,5-dichlorophenyl are good inhibitors with 3,5-dichlorophenylboronic acid as a particularly effective one (see Keller et al, Biochem. Biophys. Res. Com. 176, 1991, pp. 401-405).
It is also claimed that aryl boronic acids which have a substitution at the 3-position relative to boron are unexpectedly good reversible protease inhibitors. Especially, acetamidophenyl boronic acid is claimed to be a superior inhibitor of proteolytic enzymes (see WO 92/19707).
In WO 96/41859 substituted phenyl boronic acids are disclosed as suitable enzyme stabilizers.
It has been found that borates are reprotoxic in animals and therefore there is a demand to find alternatives which can be used to stabilize the enzymes in liquid compositions. In a particular embodiment of the present invention the liquid composition does not comprise borate or boric acid.
In EP 0 378 261 S1 an enzyme stabilization system comprising carboxylic acids for aqueous liquid detergent compositions is disclosed.